1. Field of the Invention
The present invention relates to a measuring apparatus for the speed or direction of fluid, such as air or liquid.
2. Description of the Prior Art
There are at present many types of hot anemometers for measuring the fluid speed.
The hot anemometer is formed of coiled tungsten or platinum wire to which voltage is applied so as to raise a temperature up to a predetermined degree, and comprises bridge circuits to keep constant the temperature of a sensor, thereby measuring the wind speed by the hot ray on a basis of change in voltage, current or power, following a resistance change in the sensor caused by a speed change of the fluid.
Such hot anemometer, however, is likely to disconnect its coil, is problematical in handling or its lifetime, and causes variation in the characteristic of each sensor, whereby it is required to correct an output value to meet the characteristic of each sensor and to provide an amplifier at each sensor for the multipoint measurement.
Also, it is necessary for improving the measuring accuracy to largely amplify by an amplifier a resistance value smaller in a range of change, whereby the anemometer is defective in that it is very expensive for amplification and complex in supporting a coiled hot wire and holding lead wires connected thereto.